This invention relates to a fuel injector for use in supplying fuel under pressure to a combustion space of an internal combustion engine. The invention relates, in particular, to an injector suitable for use in supplying fuel to an engine of the compression ignition type, the injector forming part of a common rail fuel system. It will be appreciated, however, that the injector may be used in other applications.
In order to reduce the levels of noise and particulate emissions produced by an engine it is desirable to provide an arrangement whereby the rate at which fuel is delivered to the engine can be controlled. It is also desirable to be able to adjust other injection characteristics, for example the spray pattern formed by the delivery of fuel by an injector.
A known fuel injector which permits this to be achieved comprises an outwardly opening valve member which is slidable within a first bore provided in a nozzle body. The valve member is provided with a second bore within which an inwardly opening valve needle is slidable, the valve needle being engageable with a seating to control fuel flow delivery through a first set of outlet openings provided in the valve member. The valve member is also provided with a second set of outlet openings in constant communication with a part of the second bore upstream of the seating, the second set of outlet openings being located such that, when the valve member adopts an inner, closed position within the first bore, the second set of outlet openings are closed by the nozzle body. When the valve member is moved outwardly to an open position, fuel within the second bore is able to flow through the second set of outlet openings into the engine cylinder.
Movement of the valve needle and the valve member is controlled by means of an actuator arrangement to permit fuel delivery through a selected one or both of the first and second sets of outlet openings, thereby enabling the fuel injection characteristic to be varied, in use. A disadvantage of this arrangement is that a relatively high leakage of fuel can occur to the engine cylinder between the nozzle body and the valve member. In addition, the components of the fuel injector are subject to relatively high stresses.
It is an object of the present invention to provide a fuel injector which permits the fuel injection characteristic to be varied, in use, and which overcomes the aforementioned disadvantages of known fuel injectors having this capability. It is a further object of the present invention to provide a fuel injector in which the fuel injection characteristic can be controlled with improved accuracy.
According to one aspect of the present invention there is provided a fuel injector comprising a nozzle body defining a first bore and an inwardly opening valve member slidable within the first bore, the valve member being engageable with a first seating to control fuel delivery through a first outlet opening provided in the nozzle body, the valve member being provided with a second bore within which an outwardly opening valve needle is slidable, the valve needle being engageable with a second seating to control fuel delivery through a second outlet opening provided in the valve needle, the fuel injector comprising first and second control chambers for fuel, whereby fuel pressure within the first and second control chambers controls movement of the valve member and the valve needle away from their respective seatings so as to permit fuel delivery through a selected outlet opening.
In such an arrangement, movement of the valve needle in an outwards direction away from the second seating permits fuel delivery through the second outlet opening and movement of the valve member away from the first seating in an inwards directions permits fuel delivery through the first outlet opening. Thus, by controlling movement of the valve member and the valve needle, and injecting fuel through a selected one or more of the first or second outlet openings, the fuel injection characteristic, for example the rate of injection of fuel, can be varied, in use.
As movement of the valve member and the valve needle is controlled by controlling fuel pressure within the first and second control chambers, rather than being controlled directly by means of an actuator arrangement, valve needle and valve member movement, and hence the fuel injection characteristic, can be controlled with improved accuracy.
The valve needle may define a flow passage for fuel which communicates with a delivery chamber such that, when the valve needle is moved away from the second seating, fuel within the delivery chamber is able to flow through the flow passage for delivery through the second outlet opening.
The force due to fuel pressure within the flow passage serves to improve the seal between the valve member and the nozzle body, and between the valve needle and the valve member, thereby reducing fuel leakage from the injector.
The delivery chamber is conveniently defined by a part of the second bore provided in the valve needle and the valve member. Conveniently, the valve member may include a guide region which serves to guide sliding movement of the valve needle within the second bore.
The valve member may have a first surface associated therewith, the first surface being exposed to fuel pressure within the first control chamber. The first surface may be carried by a first piston member which is movable with the valve member. The valve needle may have a second surface associated therewith, the second surface being exposed to fuel pressure within the second control chamber. The second surface may be carried by a second piston member which is movable with the valve needle.
The valve needle may be provided with a plurality of appropriately positioned second outlet openings. Alternatively, or in addition, the nozzle body may be provided with a plurality of appropriately positioned first outlet openings.
The fuel injector may include a third control chamber for fuel, the third control chamber communicating with the second control chamber by means of a restricted flow passage, fuel pressure within the third control chamber acting on a third surface associated with the valve needle to urge the valve needle outwardly from the second bore. In use, when fuel pressure within the second control chamber is reduced, fuel pressure within the third control chamber acting on the third surface serves to bias the valve needle away from its seating to permit fuel delivery through the second outlet opening.
According to a second aspect of the invention, there is provided a fuel injector comprising a nozzle body defining a first bore and an inwardly opening valve member slidable within the first bore, the valve member being engageable with a first seating to control fuel delivery through a first outlet opening provided in the nozzle body, the inwardly opening valve member being provided with a second bore within which an outwardly opening valve needle is slidable, the valve needle being engageable with a second seating to control fuel delivery through a second outlet opening provided in the valve needle, the valve needle defining a flow passage for fuel which communicates with a delivery chamber such that, when the valve needle is moved away from the second seating, fuel within the delivery chamber is able to flow through the flow passage for delivery through the second outlet opening.
This provides the advantage that fuel pressure within the flow passage acts in a radially outwards direction and serves to improve the fluid-tight seal between the valve member and the nozzle body and between the valve needle and the valve member, thereby reducing leakage from the fuel injector.